1. Field of the Invention
The subject matter disclosed herein relates to a diesel combustion system including an injector for furnishing fuel directly to the combustion chamber of an engine, as well as to a piston bowl with a floor which interacts with the fuel spray.
2. Discussion of the Prior Art
Designers of internal combustion engines have been confronted with ever more stringent requirements relating to fuel economy and exhaust emissions. With compression ignition engines, commonly called ‘diesel’ engines, certain exhaust emission components, including oxides of nitrogen (NOx) and soot, are more difficult to control. Moreover, alterations in engine operating parameters tending to reduce the fixation of nitrogen also generally tend to increase the amount of soot formed during the combustion process. Presently, NOx and soot are being controlled ever more tightly, and there is a need for a combustion system which will permit reasonable control of both NOx and soot.
NOx is controlled in some engines by retarding injection timing. This usually has the unfortunate effect of increasing fuel consumption. Because nitrogen fixation is a product of peak combustion temperature, it is known that NOx emissions may be reduced by lowering the peak flame temperature in an engine. This, however, can have the unfortunate effect of increasing soot produced by the engine.
FIG. 3 shows a prior art combustion chamber in which the peripheral exit angle of a piston bowl is in the range of about 81°. Fuel does not impinge upon the floor of the bowl of the combustion system. Rather, the fuel spray impacts the transition region at the outer periphery of the bowl, shown at “I”. This type of flow results in early nitrogen fixation, as well as momentum loss, which limits the recirculation of partially burned fuel and combustion products into the hotter zone of the cylinder, particularly in view of the peripheral exit angle, which is shown at II as being less than 90°, and which is not optimized to redirect and re-entrain burnt material into the hottest part of the combustion chamber.
It would be desirable to have an engine combustion system which not only permits injection timing to be advanced to a reasonable degree so as to provide good fuel economy, but also provides lower NOx and less soot.